why some object doesn't show up color
Your screenshot shows that you've added the red material to material slot 2, so I guess there is a white material in slot 1. By default the complete object gets the first material. So the easiest way would be to delete the white material from the cylinder if that's the only one you want to show up.
Another way would be (if you want different colors on the cylinder) to go into Edit Mode, select those faces that should be red and hit Apply in the Material Tab to give them the material in the second slot.